A method of producing a thin film having a biaxial crystal orientation is known from U.S. Pat. No. 5,432,151. The known method includes the steps of: depositing atoms on a substrate, the atoms having a composition corresponding to the desired thin layer; and, simultaneously to the step of depositing atoms, bombarding the deposited atoms with an energized beam, the beam being oriented with respect to the substrate within a certain angle range. This method is also called IBAD (Ion Beam Assisted Deposition), and it is conducted in an apparatus including a source for atoms and a source for an energized beam. The atoms have a composition corresponding to the desired thin film. The substrate is positioned within a common working range of the two sources such that atoms are deposited on the substrate at the same time as the atoms being deposited on the substrate are bombarded by the energized beam. The energized beam is a beam of accelerated argon ions being oriented with respect to the substrate at an angle between approximately 20° and 70°. The beam partly removes the atoms being deposited on the substrate. Especially, atoms not being located at the desired biaxial crystal orientation on the substrate are removed from the substrate. In this way, during an increase of the thickness of the layer of the respective thin film, the portions having textures which do not correspond to the desired crystal orientation are reduced, whereas the portions having the desired crystal orientation are increased.
In case of the known IBAD method, the substrate needs to be arranged within the working region of both sources for atoms and for an energized beam. Thus, there is not much room in the known apparatus, especially when the sources are located comparatively close to the substrate. The desired biaxial crystal orientation of the thin films being produced by the known method significantly depend on the thickness of the thin film. An X-ray analysis of the texture of a thin film being produced by the known IBAD method results in a full width at half maximum (phi scan) which is in accordance with a negatively sloping exponential function. A full width at half maximum of 25° is only reached when using a minimum thickness of the film of at least 500 nm. Even smaller full widths at half maximum even require substantially greater values of the layers of the thin film. Due to the fact that the increase of thickness of a thin film being produced by the IBAD method is small, the efficiency of the known IBAD method of producing thin films with the desired biaxial crystal orientation is strongly limited.
Another method of producing thin films having a biaxial crystal orientation is known from U.S. Patent Application No. 2002/0073918 A1. In contrast to the known IBAD method, the steps of depositing atoms on the substrate and the steps of bombarding the deposited atoms with an energized beam are conducted at different locations and at different points in time. At first, the atoms for the desired thin film are deposited on the substrate. In the following, the deposited atoms attain the desired biaxial crystal orientation due to the energized beam. For this purpose, a particle beam of accelerated argon ions is directed onto the thin film at an angle of approximately 55° with respect to the substrate. In this way, a texture is imprinted in the surface of the thin film, the texture corresponding to the desired biaxial crystal orientation. However, the range of the argon ions within the thin film only is a few nanometers. Thus, the desired biaxial orientation of the thin film produced by the energized beam only has a small depth. This small depth could only be increased by later anneal of the thin film to cause the crystals to grow. Even then, the known method only realizes a biaxial texture to a small extent. The full width at half maximum during an X-ray analysis (phi scan) is not substantially greater than 25°. This comparatively bad result of the desired biaxial crystal orientation is not compensated by the fact that—due to conducting the steps of depositing and of bombarding the deposited atoms with an energized beam at different points in time—these steps may also be conducted at different locations such that the source for atoms and the source for an energized beam do not interfere although their working ranges overlap in the desired way.